The present invention relates to fiber reinforced elastomers, and tires made using fiber reinforced elastomers.
In general, the presence of short fibers in a cured rubber compound results in an increase in initial or low strain (low elongation) modulus (stiffness). Concomitantly, the presence of short fibers in the rubber often times results in reduced fatigue endurance and in higher hysteretic heat build-up under periodic stresses.
Since the rubber in a rolling tire undergoes periodic deformations, for example, it is desirable that the fatigue fracture properties of a short fiber reinforced composite, used for such a purpose, be at least equal to those of the unreinforced rubber matrix.
Various discontinuous short fibers have been used to enhance stiffness (modulus) of rubber vulcanizates. For example, discontinuous cellulose fibers have been used as dispersions in rubber as disclosed in U.S. Pat. Nos. 3,697,364, 3,802,478 and 4,236,563. Other discontinuous fibers have been suggested or used such as, for example, aromatic polyamides (aramids), aliphatic polyamides (nylon), cotton, rayon, polyester, glass, carbon and steel.
Many of the polymeric fibers used in the tire art are known as fully or highly oriented short fibers. Elastomers reinforced with short fibers, for example Kevlar.RTM. pulp, demonstrate good stiffness. As the loading of Kevlar.RTM. pulp in an elastomer increases, the stiffness of the composite increases, however, the crack growth resistance decreases. Consequently, for some applications, it may not be possible to obtain a suitable balance between stiffness and crack growth resistance in an elastomer by using only fully or highly oriented short fibers.
International patent application WO 90/04617 to Allied Signal Inc. teaches the preparation of partially oriented yarns (POY short fibers) and discloses that such short fibers can be used in tires. The application does not teach that such fibers can be used in a tread base, or the specific properties desired for such use, or the fiber loading required.
Normally, where discontinuous fibers are used, the rubber composite also contains a particulate reinforcement in combination therewith.
In accordance with the invention, it is proposed that short fiber reinforced components can replace conventional components in a tire. For example, it is known in the prior art to provide an overlay ply in the crown area of tires that are subjected to high speeds. It is proposed in accordance with one embodiment of the present invention, to eliminate the need for prior art overlay fabric by using a short fiber reinforced rubber layer as the tread base, which may be calendered, or alternatively, co-extruded with the tread rubber. Co-extrusion of such material will reduce the labor required to build a tire.
Accordingly, it is an object of the present invention to provide means for reinforcing an elastomer matrix whereby a good balance of desired properties in the elastomer matrix is obtained at a minimum cost.
A tire made using the reinforced matrix of the invention is also disclosed.
Other objects of the invention will be apparent from the following description and claims.